A hearing aid may be used by one who is hard of hearing and so on.
The hearing aid comprises a microphone which may receive external sound, a speaker which transmits sound into an ear, a body portion having an electric device (including an electric battery) which may drive the microphone and the speaker, and the ear mold which may be inserted into an ear (the external auditory meatus) and may be joined to said body portion.
Whatever an efficiency of the body portion of a hearing aid may be raised, and when the ear mold cannot be adapted to a user, it gives the user an unpleasant feeling and it cannot maintain a proper tone quality. In the ear mold for the hearing aid, the problem occurs of a high pitched sound and sound leak-age (what is also called a phenomenon of a howling).
Regarding the ear mold for the hearing aid, lately, the ear mold of a custom-made hearing aid, which is produced according to the shape of the ear of a user, has been recommended as the above-mentioned ear mold. However, said custom made ear mold causes problems. For example, it gives a feeling of incompatibility for the user, and easily falls out of the user's ear. Further, it also has the know phenomenon of “howling.”
The material that ear molds have been formed out of include an MMA (methylmethacrylate) resin, for example. Lately a silicon resin has been used as the forming material. As the silicon resin can reduce a burden when in contact with the external auditory meatus, and does not cause an allergic reaction, the silicon resin can be adapted for the above-mentioned use.
For manufacturing of the custom made ear mold, generally a forming material which takes an impression, such as silicon, is inserted into the external auditory meatus of the user. After hardening, an ear impression is created. After spreading wax or the like in the surface of said ear impression, a plaster is poured into the mold of said ear impression. Said ear impression is thus made from said pattern. After removing the wax and/or paraffin wax from said ear impression, a pattern of plaster is made based on the ear impression. The forming material of the ear mold, such as the silicon resin, is poured into said pattern of plaster. After the ear mold has hardened the custom made ear mold is obtained.
Heretofore said silicon ear mold shown in FIG. 8A, was prepared by the above-mentioned method and based on an ear impression of the user. However, the silicon ear mold can also be made by as follows.
A tube 802 passes into a lead-sound-hole of the silicon ear mold 801. This tube 802 passes through said ear mold 801 as shown in FIG. 8A. The metal bush 803, as shown in FIG. 8B, fits into an end section of this tube 802. Tube 802 pulls back because the metal bush 803 is put into an end section of the silicon ear mold 801. In this case, said metal bush 803 has been used because of settlement of the above-mentioned tube 802.
However, said silicon ear mold has a disadvantage such that said tube 802 is easily moved due to instability, because said tube 802 is settled by said metal bush 803.
Also, said silicon ear mold has the disadvantage that the tube 802 is destroyed by stress which is concentrated on the above-mentioned end section of ear mold 801 when the ear mold is removed. Additionally, tube 802 also drops out from the ear mold 801.
Further, in case of small of the external auditory meatus, the tube 802 cannot maintain the necessary thickness for maintaining the rigidity of the silicon material because the tube 802 is put in the inside of an ear mold 801 and the tube 802 its own thickness.
Furthermore, if the thickness of the tube 802 is increased, the ear mold has a surplus thickness at the portion of the external auditory meatus.
On the other hand, there is provided the silicon ear mold 701 as shown in FIG. 7 which is manufactured by the previously-mentioned method. In this silicon ear mold 701, a plastics-elbow or nylon-L-tube 702 is inserted into the lead-sound-hole of silicon ear mold 701 as shown in FIG. 7. The plastics-elbow or nylon-L-tube 702 is connected with the silicon ear mold 701 by an adhesive. Namely, said plastics-elbow or nylon-L-tube 702 is fixed by the glued-part 703 of said plastics-elbow or nylon-L-tube 702 on the inside of said silicon ear mold 701. In said silicon ear mold 701, as shown in the drawings, an end portion of the plastics-elbow or nylon-L-tube 702 is connected by an adhesive to the inside of said silicon ear mold 701.
As shown in the drawings, the other end portion of the tube for joining the hearing aid (vinyl tube) 704 may be joined with said plastics-elbow or nylon-L-tube 702.
In said silicon ear mold, the plastics-elbow or nylon-L-tube 702 is not secure inside the silicon ear mold 701. Said plastics-elbow or nylon-L-tube 702 is cut off.
Therefore, said plastics-elbow or nylon-L-tube 702 can be in the case of a small external auditory meatus. Said plastics-elbow or nylon-L-tube 702 is different from said silicon ear mold 801 as previously mentioned and as shown in FIG. 8.
For the reason of stiffness of said vinyl tube 704, which increases with use, it is necessary to periodically change said vinyl tube 704. Vinyl tube 704 is not a single body, and is independent from said ear mold 701, through the intervention of said plastics-elbow or nylon-L-tube 702. Thus, the exchange is easy.
But, said silicon ear mold has a problem that the between the plastics-elbow or nylon-L-tube 702 and the earl mold 701 decreases. Consequently, the plastics-elbow or nylon-L-tube 702 detaches easily and drops out from said ear mold 701. As such, the phenomenon of howling occurs due to sound leaking-out.